The present invention relates generally to the field of control and monitoring networks, such as those used for industrial applications. More particularly, the invention relates to a technique for providing power to networked devices and for switching the application power to a secondary or backup supply in the event of a malfunction in a normal device power supply, such as over the network.
A range of networks are known and are presently in use for industrial control and monitoring operations. In many such systems, fairly complex monitoring and control functions are designed around specific networks components which are linked to one another via a power and data signal network. For example, in industrial manufacturing, material handling, and other applications, a wide range of prime movers, typically electric motors, as well as actuators, valves, and so forth, may be operated based upon signals from networked devices. The status of the physical system is then indicated back to control devices via input and output modules. Based upon such status signals, the processes may be regulated and controlled to a high degree with enhanced performance and efficiency.
Devices networked in industrial settings may include industrial computers, typically in the form of programmable logic devices, as well as microcontrollers, switch gear, protective devices, and the like. In a motor control center, for example, motor starters, motor controllers, contactors, circuit interrupters, circuit breakers, and so forth provide for regulation of speeds of electric motors used in complex manufacturing and material handling operations. The function of the various components is coordinated so as to provide for operation during normal service, as well as for some type of failure mode operation, or “controlled shutdown”. In certain industrial networks of this type, both power for operation of these devices, and data signals for exchanging command and feedback signals, are provided via the network.
Where operation of a networked monitoring or control component relies upon application of power and data signals via a network connection, difficulties can arise if a power supply is interrupted or if the distribution media become severed or inoperative. While increasingly intelligent devices are provided in such networks, enabling preprogramming of certain failure modes from a logical standpoint, a loss of power to the devices may jeopardize the ability to carry out such operations. In certain known systems, for example, cabling is employed for applying both direct current power and data signals to devices. Certain failure modes are pre-programmed into the devices for their logical operation, but a loss of power from the network can result in the inability of the device to perform its failure mode functions, particularly over an extended period of time. Similarly, in a network setting certain devices may be programmed for some type of “controlled shutdown,” but that typically requires power during at least a limited duration for operation of the devices.
There is a need, therefore, for a technique that allows for control and monitoring functions to be maintained in such networks even if power from the network becomes interrupted or is insufficient to provide for normal operation of the networked devices. There is a particular need for a technique which offers an array of backup power sources, depending upon the backup power availability, and which can be interfaced with conventional network cabling and power sources to afford a reliable backup power supply in the event of loss of network power.